a) Field of the invention
The present invention relates to a finder optical system of the real image type which is suited for use with compact cameras such as photographic cameras and video cameras.
b) Description of the prior art
Since most of the photographic lens systems used for compact cameras have wide field angles, it was necessary to design finder optical systems which also had wide field angles like those of the photographic lens systems. These conventional finder optical systems were mostly Albada finders and the inverse Galilean finders of the virtual image type which could easily have relatively wide field angles.
However, these finder optical systems of the virtual image type had a common defects that they obliged to enlarge diameters on the lens components arranged on the object side therein, and that they lowered legibility on the display members which indicate visual field frames and so on.
Accordingly, the finder optical systems of the real image type such as Keplerian optical finder optical systems have recently attracted attention once again and widely been adopted as exemplified by the optical finder systems disclosed by Japanese Preliminary Utility Model Publication No. Sho 63-30812 and Japanese Preliminary Patent Publication Nos. Sho 63-44616, Sho 63-44617, Hei 1-154114 and Hei 1-255825.
However, the above-mentioned conventional finder optical systems of the real image type pose a common problem: they inevitably use a large numbers of parts, and have complicated compositions and large external designs.